Package org.codehaus.groovy.vmplugin.v8

## Class PluginDefaultGroovyMethods

- java.lang.Object
- - org.codehaus.groovy.runtime.DefaultGroovyMethodsSupport
  - - org.codehaus.groovy.vmplugin.v8.PluginDefaultGroovyMethods

-     public class PluginDefaultGroovyMethods
      extends DefaultGroovyMethodsSupport

  Defines new Groovy methods which appear on standard Java 8 classes within the Groovy environment.
  Since:
    2.5.0

- - ### Method Summary

    All Methods Static Methods Concrete Methods Deprecated Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `static boolean` | `asBoolean​(Optional<?> optional)` | Coerce an `Optional` instance to a `boolean` value.
    `static <S,​T> Future<T>` | `collect​(Future<S> self, Closure<T> transform)` | Returns a Future asynchronously returning a transformed result.
    `static <S,​T> Optional<T>` | `collect​(Optional<S> self, Closure<T> transform)` | If the optional contains a value, returns an optional containing the transformed value obtained using the `transform` closure or otherwise an empty optional.
    `static <T> Optional<T>` | `filter​(Optional<?> self, Class<T> type)` | Tests given value against specified type and changes generics of result.
    `static OptionalDouble` | `filter​(OptionalDouble self, DoublePredicate test)` | If a value is present in the `OptionalDouble`, tests the value using the given predicate and returns the optional if the test returns true or empty otherwise.
    `static OptionalInt` | `filter​(OptionalInt self, IntPredicate test)` | If a value is present in the `OptionalInt`, tests the value using the given predicate and returns the optional if the test returns true or else empty.
    `static OptionalLong` | `filter​(OptionalLong self, LongPredicate test)` | If a value is present in the `OptionalLong`, tests the value using the given predicate and returns the optional if the test returns true or else empty.
    `static double` | `get​(OptionalDouble self)` | If a value is present in the `OptionalDouble`, returns the value, otherwise throws `NoSuchElementException`.
    `static int` | `get​(OptionalInt self)` | If a value is present in the `OptionalInt`, returns the value, otherwise throws `NoSuchElementException`.
    `static long` | `get​(OptionalLong self)` | If a value is present in the `OptionalLong`, returns the value, otherwise throws `NoSuchElementException`.
    `static StringBuilder` | `leftShift​(StringBuilder self, Object value)` | Overloads the left shift operator to provide an easy way to append multiple objects as string representations to a StringBuilder.
    `static <T> OptionalDouble` | `mapToDouble​(Optional<T> self, ToDoubleFunction<? super T> mapper)` | If a value is present in the `OptionalDouble`, returns an `OptionalDouble` consisting of the result of applying the given function to the value or else empty.
    `static <T> OptionalInt` | `mapToInt​(Optional<T> self, ToIntFunction<? super T> mapper)` | If a value is present in the `OptionalInt`, returns an `OptionalInt` consisting of the result of applying the given function to the value or else empty.
    `static <T> OptionalLong` | `mapToLong​(Optional<T> self, ToLongFunction<? super T> mapper)` | If a value is present in the `OptionalLong`, returns an `OptionalLong` consisting of the result of applying the given function to the value or else empty.
    `static <T> Optional<T>` | `mapToObj​(OptionalDouble self, DoubleFunction<? extends T> mapper)` | If a value is present in the `OptionalDouble`, returns an `Optional` consisting of the result of applying the given function to the value or else empty.
    `static <T> Optional<T>` | `mapToObj​(OptionalInt self, IntFunction<? extends T> mapper)` | If a value is present in the `OptionalInt`, returns an `Optional` consisting of the result of applying the given function to the value or else empty.
    `static <T> Optional<T>` | `mapToObj​(OptionalLong self, LongFunction<? extends T> mapper)` | If a value is present in the `OptionalLong`, returns an `Optional` consisting of the result of applying the given function to the value or else empty.
    `static Object` | `next​(Enum self)` | Overloads the `++` operator for enums.
    `static <T> Optional<T>` | `orOptional​(Optional<T> self, Supplier<? extends Optional<? extends T>> supplier)` | Provide similar functionality to JDK9 `or` on JDK8.
    `static String` | `plus​(StringBuilder self, String value)` | Appends a String to this StringBuilder.
    `static Object` | `previous​(Enum self)` | Overloads the `--` operator for enums.
    `static void` | `putAt​(StringBuilder self, EmptyRange range, Object value)` | Supports the range subscript operator for StringBuilder.
    `static void` | `putAt​(StringBuilder self, IntRange range, Object value)` | Supports the range subscript operator for StringBuilder.
    `static int` | `size​(StringBuilder self)` | Deprecated.
    `static Stream<Boolean>` | `stream​(boolean[] self)` | Returns a sequential `Stream` with the specified array as its source.
    `static Stream<Byte>` | `stream​(byte[] self)` | Returns a sequential `Stream` with the specified array as its source.
    `static Stream<Character>` | `stream​(char[] self)` | Returns a sequential `Stream` with the specified array as its source.
    `static Stream<Double>` | `stream​(double[] self)` | Returns a sequential `Stream` with the specified array as its source.
    `static Stream<Float>` | `stream​(float[] self)` | Returns a sequential `Stream` with the specified array as its source.
    `static Stream<Integer>` | `stream​(int[] self)` | Returns a sequential `Stream` with the specified array as its source.
    `static Stream<Long>` | `stream​(long[] self)` | Returns a sequential `Stream` with the specified array as its source.
    `static Stream<Short>` | `stream​(short[] self)` | Returns a sequential `Stream` with the specified array as its source.
    `static <T> Stream<T>` | `stream​(Iterable<T> self)` | Returns a sequential `Stream` with the specified element(s) as its source.
    `static <T> Stream<T>` | `stream​(Enumeration<T> self)` | Returns a sequential `Stream` with the specified element(s) as its source.
    `static <T> Stream<T>` | `stream​(Iterator<T> self)` | Returns a sequential `Stream` with the specified element(s) as its source.
    `static <T> Stream<T>` | `stream​(Optional<T> self)` | If a value is present in the `Optional`, returns a `Stream` with the value as its source or else an empty stream.
    `static DoubleStream` | `stream​(OptionalDouble self)` | If a value is present in the `OptionalDouble`, returns a `DoubleStream` with the value as its source or else an empty stream.
    `static IntStream` | `stream​(OptionalInt self)` | If a value is present in the `OptionalInt`, returns an `IntStream` with the value as its source or else an empty stream.
    `static LongStream` | `stream​(OptionalLong self)` | If a value is present in the `OptionalLong`, returns a `LongStream` with the value as its source or else an empty stream.
    `static <T> Stream<T>` | `stream​(Spliterator<T> self)` | Returns a sequential `Stream` with the specified element(s) as its source.
    `static <T> Stream<T>` | `stream​(NullObject self)` | Returns an empty sequential `Stream`.
    `static <T> Stream<T>` | `stream​(T self)` | Returns a sequential `Stream` containing a single element.
    `static <T> Stream<T>` | `stream​(T[] self)` | Returns a sequential `Stream` with the specified array as its source.
    `static <T> T[]` | `toArray​(Stream<? extends T> self, Class<T> type)` | Returns an array containing the elements of the stream.
    `static <T> List<T>` | `toList​(BaseStream<T,​? extends BaseStream> self)` | Accumulates the elements of stream into a new List.
    `static <T> List<T>` | `toList​(Stream<T> self)` | Accumulates the elements of stream into a new List.
    `static <T> Set<T>` | `toSet​(BaseStream<T,​? extends BaseStream> self)` | Accumulates the elements of stream into a new Set.
    `static <T> Set<T>` | `toSet​(Stream<T> self)` | Accumulates the elements of stream into a new Set.

    - ### Methods inherited from class org.codehaus.groovy.runtime.DefaultGroovyMethodsSupport

      `cloneSimilarCollection, cloneSimilarMap, closeQuietly, closeWithWarning, createSimilarArray, createSimilarCollection, createSimilarCollection, createSimilarCollection, createSimilarList, createSimilarMap, createSimilarOrDefaultCollection, createSimilarQueue, createSimilarSet, normaliseIndex, sameType, subListBorders, subListBorders, writeUTF16BomIfRequired, writeUTF16BomIfRequired, writeUTF16BomIfRequired, writeUTF16BomIfRequired`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Method Detail

    - #### asBoolean

          public static boolean asBoolean​(Optional<?> optional)

      Coerce an `Optional` instance to a `boolean` value.

           assert !Optional.empty().asBoolean()
           assert Optional.of(1234).asBoolean()

      Parameters:
        `optional` - the Optional
      Returns:
        `true` if a value is present, otherwise `false`
      Since:
        2.5.0

    - #### get

          public static int get​(OptionalInt self)

      If a value is present in the `OptionalInt`, returns the value, otherwise throws `NoSuchElementException`.

           assert OptionalInt.of(1234).get() == 1234

      Since:
        3.0.0

    - #### get

          public static long get​(OptionalLong self)

      If a value is present in the `OptionalLong`, returns the value, otherwise throws `NoSuchElementException`.

           assert OptionalLong.of(1234L).get() == 1234L

      Since:
        3.0.0

    - #### get

          public static double get​(OptionalDouble self)

      If a value is present in the `OptionalDouble`, returns the value, otherwise throws `NoSuchElementException`.

           assert OptionalDouble.of(Math.PI).get() == Math.PI

      Since:
        3.0.0

    - #### filter

          public static <T> Optional<T> filter​(Optional<?> self,
                                               Class<T> type)

      Tests given value against specified type and changes generics of result. This is equivalent to: `self.filter(it -> it instanceof Type).map(it -> (Type) it)`

           assert !Optional.empty().filter(Number).isPresent()
           assert !Optional.of('x').filter(Number).isPresent()
           assert Optional.of(1234).filter(Number).isPresent()
           assert Optional.of(1234).filter(Number).get().equals(1234)

      Since:
        3.0.0

    - #### filter

          public static OptionalInt filter​(OptionalInt self,
                                           IntPredicate test)

      If a value is present in the `OptionalInt`, tests the value using the given predicate and returns the optional if the test returns true or else empty.

           assert !OptionalInt.empty().filter(i -> true).isPresent()
           assert  OptionalInt.of(1234).filter(i -> true).isPresent()
           assert !OptionalInt.of(1234).filter(i -> false).isPresent()
           assert  OptionalInt.of(1234).filter(i -> true).getAsInt() == 1234

      Since:
        3.0.0

    - #### filter

          public static OptionalLong filter​(OptionalLong self,
                                            LongPredicate test)

      If a value is present in the `OptionalLong`, tests the value using the given predicate and returns the optional if the test returns true or else empty.

           assert !OptionalLong.empty().filter(n -> true).isPresent()
           assert  OptionalLong.of(123L).filter(n -> true).isPresent()
           assert !OptionalLong.of(123L).filter(n -> false).isPresent()
           assert  OptionalLong.of(123L).filter(n -> true).getAsLong() == 123L

      Since:
        3.0.0

    - #### filter

          public static OptionalDouble filter​(OptionalDouble self,
                                              DoublePredicate test)

      If a value is present in the `OptionalDouble`, tests the value using the given predicate and returns the optional if the test returns true or empty otherwise.

           assert !OptionalDouble.empty().filter(n -> true).isPresent()
           assert  OptionalDouble.of(Math.PI).filter(n -> true).isPresent()
           assert !OptionalDouble.of(Math.PI).filter(n -> false).isPresent()
           assert  OptionalDouble.of(Math.PI).filter(n -> true).getAsDouble() == Math.PI

      Since:
        3.0.0

    - #### mapToObj

          public static <T> Optional<T> mapToObj​(OptionalInt self,
                                                 IntFunction<? extends T> mapper)

      If a value is present in the `OptionalInt`, returns an `Optional` consisting of the result of applying the given function to the value or else empty.

           assert !OptionalInt.empty().mapToObj(x -> new Object()).isPresent()
           assert  OptionalInt.of(1234).mapToObj(x -> new Object()).isPresent()
           assert !OptionalInt.of(1234).mapToObj(x -> null).isPresent()
           assert  OptionalInt.of(1234).mapToObj(Integer::toString).get() == '1234'

      Since:
        3.0.0

    - #### mapToObj

          public static <T> Optional<T> mapToObj​(OptionalLong self,
                                                 LongFunction<? extends T> mapper)

      If a value is present in the `OptionalLong`, returns an `Optional` consisting of the result of applying the given function to the value or else empty.

           assert !OptionalLong.empty().mapToObj(x -> new Object()).isPresent()
           assert  OptionalLong.of(123L).mapToObj(x -> new Object()).isPresent()
           assert !OptionalLong.of(123L).mapToObj(x -> null).isPresent()
           assert  OptionalLong.of(1234L).mapToObj(Long::toString).get() == '1234'

      Since:
        3.0.0

    - #### mapToObj

          public static <T> Optional<T> mapToObj​(OptionalDouble self,
                                                 DoubleFunction<? extends T> mapper)

      If a value is present in the `OptionalDouble`, returns an `Optional` consisting of the result of applying the given function to the value or else empty.

           assert !OptionalDouble.empty().mapToObj(x -> new Object()).isPresent()
           assert  OptionalDouble.of(Math.PI).mapToObj(x -> new Object()).isPresent()
           assert !OptionalDouble.of(Math.PI).mapToObj(x -> null).isPresent()
           assert  OptionalDouble.of(Math.PI).mapToObj(Double::toString).get().startsWith('3.14')

      Since:
        3.0.0

    - #### mapToInt

          public static <T> OptionalInt mapToInt​(Optional<T> self,
                                                 ToIntFunction<? super T> mapper)

      If a value is present in the `OptionalInt`, returns an `OptionalInt` consisting of the result of applying the given function to the value or else empty.

           assert !Optional.empty().mapToInt(x -> 42).isPresent()
           assert  Optional.of('x').mapToInt(x -> 42).getAsInt() == 42

      Since:
        3.0.0

    - #### mapToLong

          public static <T> OptionalLong mapToLong​(Optional<T> self,
                                                   ToLongFunction<? super T> mapper)

      If a value is present in the `OptionalLong`, returns an `OptionalLong` consisting of the result of applying the given function to the value or else empty.

           assert !Optional.empty().mapToLong(x -> 42L).isPresent()
           assert  Optional.of('x').mapToLong(x -> 42L).getAsLong() == 42L

      Since:
        3.0.0

    - #### mapToDouble

          public static <T> OptionalDouble mapToDouble​(Optional<T> self,
                                                       ToDoubleFunction<? super T> mapper)

      If a value is present in the `OptionalDouble`, returns an `OptionalDouble` consisting of the result of applying the given function to the value or else empty.

           assert !Optional.empty().mapToDouble(x -> Math.PI).isPresent()
           assert  Optional.of('x').mapToDouble(x -> Math.PI).getAsDouble() == Math.PI

      Since:
        3.0.0

    - #### collect

          public static <S,​T> Optional<T> collect​(Optional<S> self,
                                                        Closure<T> transform)

      If the optional contains a value, returns an optional containing the transformed value obtained using the `transform` closure or otherwise an empty optional.

           assert Optional.of("foobar").collect{ it.size() }.get() == 6
           assert !Optional.empty().collect{ it.size() }.isPresent()

      Parameters:
        `self` - an Optional
        `transform` - the closure used to transform the optional value if present
      Returns:
        an Optional containing the transformed value or empty if the optional is empty or the transform returns null
      Since:
        3.0.0

    - #### collect

          public static <S,​T> Future<T> collect​(Future<S> self,
                                                      Closure<T> transform)

      Returns a Future asynchronously returning a transformed result.

           import java.util.concurrent.*
           def executor = Executors.newSingleThreadExecutor()
           Future foobar = executor.submit{ "foobar" }
           Future foobarSize = foobar.collect{ it.size() }
           assert foobarSize.get() == 6
           executor.shutdown()

      Parameters:
        `self` - a Future
        `transform` - the closure used to transform the Future value
      Returns:
        a Future allowing the transformed value to be obtained asynchronously
      Since:
        3.0.0

    - #### next

          public static Object next​(Enum self)

      Overloads the `++` operator for enums. It will invoke Groovy's default next behaviour for enums that do not have their own next method.
      Parameters:
        `self` - an Enum
      Returns:
        the next defined enum from the enum class
      Since:
        1.5.2

    - #### previous

          public static Object previous​(Enum self)

      Overloads the `--` operator for enums. It will invoke Groovy's default previous behaviour for enums that do not have their own previous method.
      Parameters:
        `self` - an Enum
      Returns:
        the previous defined enum from the enum class
      Since:
        1.5.2

    - #### size

          @Deprecated
          public static int size​(StringBuilder self)

      Deprecated.
      Provides the standard Groovy `size()` method for `StringBuilder`.
      Parameters:
        `self` - a StringBuilder
      Returns:
        the length of the StringBuilder
      Since:
        1.5.2
      See Also:
        `StringGroovyMethods.size(CharSequence)`

    - #### leftShift

          public static StringBuilder leftShift​(StringBuilder self,
                                                Object value)

      Overloads the left shift operator to provide an easy way to append multiple objects as string representations to a StringBuilder.
      Parameters:
        `self` - a StringBuilder
        `value` - a value to append
      Returns:
        the StringBuilder on which this operation was invoked
      Since:
        1.5.2

    - #### putAt

          public static void putAt​(StringBuilder self,
                                   IntRange range,
                                   Object value)

      Supports the range subscript operator for StringBuilder. Index values are treated as characters within the builder.
      Parameters:
        `self` - a StringBuilder
        `range` - a Range
        `value` - the object that's toString() will be inserted
      Since:
        1.5.2

    - #### putAt

          public static void putAt​(StringBuilder self,
                                   EmptyRange range,
                                   Object value)

      Supports the range subscript operator for StringBuilder.
      Parameters:
        `self` - a StringBuilder
        `range` - a Range
        `value` - the object that's toString() will be inserted
      Since:
        1.5.2

    - #### plus

          public static String plus​(StringBuilder self,
                                    String value)

      Appends a String to this StringBuilder.
      Parameters:
        `self` - a StringBuilder
        `value` - a String
      Returns:
        a String
      Since:
        1.5.2

    - #### toArray

          public static <T> T[] toArray​(Stream<? extends T> self,
                                        Class<T> type)

      Returns an array containing the elements of the stream.

           import static groovy.test.GroovyAssert.shouldFail

           assert Arrays.equals([].stream().toArray(Object), new Object[0])
           assert Arrays.equals([].stream().toArray(String), new String[0])
           assert Arrays.equals([].stream().toArray(String[]), new String[0][])
           assert Arrays.equals(['x'].stream().toArray(Object), ['x'].toArray())
           assert Arrays.equals(['x'].stream().toArray(String), ['x'] as String[])
           assert Arrays.deepEquals([['x'] as String[]].stream().toArray(String[]), [['x'] as String[]] as String[][])
           assert Arrays.equals(['x'].stream().toArray(CharSequence), ['x'] as CharSequence[])

           shouldFail(ArrayStoreException) {
               ['x'].stream().toArray(Thread)
           }

           shouldFail(IllegalArgumentException) {
               ['x'].stream().toArray((Class) null)
           }

           // Stream#toArray(IntFunction) should still be used for closure literal:
           assert Arrays.equals(['x'].stream().toArray { n -> new String[n] }, ['x'] as String[])

           // Stream#toArray(IntFunction) should still be used for method reference:
           assert Arrays.equals(['x'].stream().toArray(String[]::new), ['x'] as String[])

      Parameters:
        `self` - the stream
        `type` - the array element type
      Since:
        3.0.4

    - #### toList

          public static <T> List<T> toList​(Stream<T> self)

      Accumulates the elements of stream into a new List.
      Type Parameters:
        `T` - the type of element
      Parameters:
        `self` - the stream
      Returns:
        a new `java.util.List` instance
      Since:
        2.5.0

    - #### toSet

          public static <T> Set<T> toSet​(Stream<T> self)

      Accumulates the elements of stream into a new Set.
      Type Parameters:
        `T` - the type of element
      Parameters:
        `self` - the stream
      Returns:
        a new `java.util.Set` instance
      Since:
        2.5.0

    - #### toList

          public static <T> List<T> toList​(BaseStream<T,​? extends BaseStream> self)

      Accumulates the elements of stream into a new List.
      Type Parameters:
        `T` - the type of element
      Parameters:
        `self` - the `java.util.stream.BaseStream`
      Returns:
        a new `java.util.List` instance
      Since:
        2.5.0

    - #### toSet

          public static <T> Set<T> toSet​(BaseStream<T,​? extends BaseStream> self)

      Accumulates the elements of stream into a new Set.
      Type Parameters:
        `T` - the type of element
      Parameters:
        `self` - the `java.util.stream.BaseStream`
      Returns:
        a new `java.util.Set` instance
      Since:
        2.5.0

    - #### stream

          public static <T> Stream<T> stream​(NullObject self)

      Returns an empty sequential `Stream`.

           def item = null
           assert item.stream().toList() == []
           assert !item.stream().findFirst().isPresent()

      Since:
        3.0.0

    - #### stream

          public static <T> Stream<T> stream​(T self)

      Returns a sequential `Stream` containing a single element.

           def item = 'string'
           assert item.stream().toList() == ['string']
           assert item.stream().findFirst().isPresent()

      Since:
        3.0.0

    - #### stream

          public static <T> Stream<T> stream​(T[] self)

      Returns a sequential `Stream` with the specified array as its source.
      Type Parameters:
        `T` - The type of the array elements
      Parameters:
        `self` - The array, assumed to be unmodified during use
      Returns:
        a `Stream` for the array
      Since:
        2.5.0

    - #### stream

          public static Stream<Integer> stream​(int[] self)

      Returns a sequential `Stream` with the specified array as its source.
      Parameters:
        `self` - The array, assumed to be unmodified during use
      Returns:
        a `Stream` for the array
      Since:
        2.5.0

    - #### stream

          public static Stream<Long> stream​(long[] self)

      Returns a sequential `Stream` with the specified array as its source.
      Parameters:
        `self` - The array, assumed to be unmodified during use
      Returns:
        a `Stream` for the array
      Since:
        2.5.0

    - #### stream

          public static Stream<Double> stream​(double[] self)

      Returns a sequential `Stream` with the specified array as its source.
      Parameters:
        `self` - The array, assumed to be unmodified during use
      Returns:
        a `Stream` for the array
      Since:
        2.5.0

    - #### stream

          public static Stream<Character> stream​(char[] self)

      Returns a sequential `Stream` with the specified array as its source.
      Parameters:
        `self` - The array, assumed to be unmodified during use
      Returns:
        a `Stream` for the array
      Since:
        2.5.0

    - #### stream

          public static Stream<Byte> stream​(byte[] self)

      Returns a sequential `Stream` with the specified array as its source.
      Parameters:
        `self` - The array, assumed to be unmodified during use
      Returns:
        a `Stream` for the array
      Since:
        2.5.0

    - #### stream

          public static Stream<Short> stream​(short[] self)

      Returns a sequential `Stream` with the specified array as its source.
      Parameters:
        `self` - The array, assumed to be unmodified during use
      Returns:
        a `Stream` for the array
      Since:
        2.5.0

    - #### stream

          public static Stream<Boolean> stream​(boolean[] self)

      Returns a sequential `Stream` with the specified array as its source.
      Parameters:
        `self` - The array, assumed to be unmodified during use
      Returns:
        a `Stream` for the array
      Since:
        2.5.0

    - #### stream

          public static Stream<Float> stream​(float[] self)

      Returns a sequential `Stream` with the specified array as its source.
      Parameters:
        `self` - The array, assumed to be unmodified during use
      Returns:
        a `Stream` for the array
      Since:
        2.5.0

    - #### stream

          public static <T> Stream<T> stream​(Enumeration<T> self)

      Returns a sequential `Stream` with the specified element(s) as its source.

           def tokens = new StringTokenizer('one two')
           assert tokens.stream().toList() == ['one', 'two']

      Since:
        3.0.0

    - #### stream

          public static <T> Stream<T> stream​(Iterable<T> self)

      Returns a sequential `Stream` with the specified element(s) as its source.

           class Items implements Iterable {
             Iterator iterator() {
               ['one', 'two'].iterator()
             }
           }
           def items = new Items()
           assert items.stream().toList() == ['one', 'two']

      Since:
        3.0.0

    - #### stream

          public static <T> Stream<T> stream​(Iterator<T> self)

      Returns a sequential `Stream` with the specified element(s) as its source.

           [].iterator().stream().toList().isEmpty()
           ['one', 'two'].iterator().stream().toList() == ['one', 'two']

      Since:
        3.0.0

    - #### stream

          public static <T> Stream<T> stream​(Spliterator<T> self)

      Returns a sequential `Stream` with the specified element(s) as its source.

           [].spliterator().stream().toList().isEmpty()
           ['one', 'two'].spliterator().stream().toList() == ['one', 'two']

      Since:
        3.0.0

    - #### stream

          public static <T> Stream<T> stream​(Optional<T> self)

      If a value is present in the `Optional`, returns a `Stream` with the value as its source or else an empty stream.
      Since:
        3.0.0

    - #### stream

          public static IntStream stream​(OptionalInt self)

      If a value is present in the `OptionalInt`, returns an `IntStream` with the value as its source or else an empty stream.
      Since:
        3.0.0

    - #### stream

          public static LongStream stream​(OptionalLong self)

      If a value is present in the `OptionalLong`, returns a `LongStream` with the value as its source or else an empty stream.
      Since:
        3.0.0

    - #### stream

          public static DoubleStream stream​(OptionalDouble self)

      If a value is present in the `OptionalDouble`, returns a `DoubleStream` with the value as its source or else an empty stream.
      Since:
        3.0.0

    - #### orOptional

          public static <T> Optional<T> orOptional​(Optional<T> self,
                                                   Supplier<? extends Optional<? extends T>> supplier)

      Provide similar functionality to JDK9 `or` on JDK8.